1. Field of the Invention
The present invention relates to a motor-driven fluid pump adapted for delivering fluid into a vessel to be pressurized thereby, and more particularly to such a motor-driven fluid pump provided with a release port for rapidly releasing the pressurized fluid out of the vessel.
2. Description of the Prior Art
In recent years, there have been a growing demand of providing an automated blood pressure measuring device which incorporates a motor-driven fluid pump for feeding pressurized air into an inflatable cuff to be wrapped around the arm of the subject. One such fluid pump for the blood pressure measuring device is disclosed in Japanese Pat. Pub. No. 60-40293 in which a reversible motor has its output shaft connected to a diaphragm member defining a pump chamber through the driving linkage capable of translating the rotary motion of the motor into corresponding reciprocating motion of the diaphragm and vice versa. The driving linkage also connects the motor output shaft to a release valve in such a way as to keep the release valve closed in response to the motor being driven to rotate in the forward direction of pumping up the cuff pressure and to open the release valve in response to the motor being driven to rotate in the reverse direction, allowing a rapid discharge of the pressurized air from the cuff in an automated manner of reversing the motor. In this prior device, when the motor is stopped after attaining a sufficient increase of the cuff pressure with the diaphragm being held in a position of minimizing the volume of the pump chamber, the diaphragm will receive a counter force from the pressurized air to be forced back to its opposite position of maximizing the volume of the pump chamber. Upon this occurrence, the reciprocating motion of the diaphragm may cause the motor output shaft to rotate in the reverse direction through the driving linkage permitting the reverse translation of the reciprocating motion of the diaphragm into the rotating motion of the motor, resulting in an unintended opening of the release valve and therefore rendering the blood pressure measurement totally inoperative. This poses a critical problem in adapting the motor-driven fluid pump for an automated blood pressure measuring device. It is therefore highly desirable for the motor-driven fluid pump of this application to prevent the accidental opening of the release valve while enabling the release valve to be actuated in response to the reversal of the motor.